Process for crimping filaments at the spinneret face



J. MYLO 3,359,356

PROCESS FOR CRIMPING PILAMENTS AT THE SPINNERET FACE Dec. 19, 1967 FiledMarch 2, 1964 FIG. I.

INVENTOR JOHN MYLO ATTORNEY United States Patent 3,359,356 PROCESS FORCRIMPING FILAMENTS AT THE SPINNERET FACE John Mylo, Athens, Ala.,assignor to Monsanto Company, a corporation of Delaware Filed Mar. 2,1964, Ser. No. 348,747 Claims. (Cl. 264-168) ABSTRACT OF THE DISCLOSUREFilaments are crimped during the spinning process by drawing thefilaments from the spinneret at an acute angle therewith to impart apreferential arrangement of the molecular structure to one side of saidfilaments prior to their becoming completely coagulated or solidifiedand thereafter subjecting them to heat to develop a crimped condition.

This invention relates to the production of textile filaments from athermoplastic polymer and, more particularly, this invention relates toa process for establishing a preferential molecular orientation alongone side of the filament axis whereby a permanent crimp retentivity isimparted to said filaments.

In the manufacture of continuous filaments from a fiberformingthermoplastic material such as acrylonitrile polymers and copolymers,the filaments must be subjected to some type of special treatment in anattempt to overcome the lack of interfilamentary cohesion exhibited bythe newly formed filaments to thereby render such filaments suitable forsubsequent processing thereof. Several methods which are too numerous todiscuss herein have been utilized for improving interfilament cohesionby imparting a crimped or curled condition to continuous syntheticfilaments. The basic principle employed by all of the most commonly usedmethods, which are referred to generally as mechanical processes, isessentially the same except for composite filaments formed fromfiber-forming thermoplastic materials having different shrinkagecharacteristics. The mechanical processes comprise deformation of thespun filaments by some type mechanical aparatus to reorient themolecular structure of said filaments for the purpose of impartingthereto a memory of the deformation experienced previously by thefilaments. For example, the deformation or crinkle is imposedmechanically by means of intermeshing gear-like elements; by drawing thefilaments over a dull knifed edge; by means of a stuffer box; or bytwisting the yarns, setting the twist, and then removing the twist.

A plastic memory or crimped condition in the filaments is achievedthrough the well known process of heating the filaments a selectedamount prior to mechanically crimping said filaments. The deformation ofthe filaments while heated causes a rearrangement of the moleculestherein. If the filaments are cooled slightly to reduce the plasticitythereof in the absence of tension, the crimp will be set and therebyretained. However, if a tension is imposed on the filaments during thecooling cycle the crimp will be removed but may be redeveloped byannealing the filaments in the absence of tension.

Some apparent limitations are imposed by the above discussed methods. Insome cases it is not practical because of the investment in specialequipment required. In other instances the use of heat and softeningagents is undesirable because of their efiect on the physical propertiesof the filaments. Another serious limitation is that the molecularrearrangement caused by the mechanical deformations irnparted to thefilaments results in a lot of broken ends occurring in the filamentbundle. These broken ends, if too frequent, render the tow unsuitablefor ice processing on textile machinery such as the Pacific Converter.Perhaps the most serious problem encountered with filaments crimped bythe known methods occurs during subsequent processing steps such asdyeing in which the crimped filaments elongate to the extent thatsubstantially all of the crimp is removed from said filaments.Obviously, this characteristic imposes a serious limitation upon thedyeing of textured acrylic fibers.

Although the known methods are used extensively, it would be highlydesirable to provide a method for producing textile filaments having apermanent plastic memory and being free from damage attributable tomechanical crimping processes.

It is therefore an object of the present invention to provide animproved method of imparting a potential crinkled or curled condition tofilaments formed from fiber-forming thermoplastic materials andparticularly acrylonitrile polymers and copolymers.

Another object of the present invention is to provide a method forproducing, during normal spinning operations, textile filaments having apermanent plastic memory which is not destroyed by subsequent heatingand processing thereof.

A further object of the present invention is to impart a potentialcurliness, which may be developed later into a permanent crimp, tosynthetic filaments spun from a conventional spinneret by a novelprocess.

Still .another object of this invention is to provide a novel method ofproducing potentially crimped filaments having a permanent plasticmemory during the usual course of production with a minimum investmentin additional equipment.

Yet another object of the invention is to provide a novel method oforienting the molecular structure of spun synthetic filaments during thespinning process in a preferential manner whereupon the filaments willexhibit uniform, regularly spaced helixes around the longitudinal axisthereof when heated.

Other objects and advantages of the invention will be apparent from thedescription that follows.

The novel filamentary products of this invention are produced by the wetspinning process in which a solution comprising essentially athermoplastic filament-forming material dissolved in an organic solventor solvent mixture is extruded in the form of fine streams through aspinneret into a coagulating bath to form shaped filaments which aredrawn from the spinneret at an angle across the face thereof.

The filaments produced in accordance with the present invention arecharacterized by a combination of properties unique in the manufactureof artificial thermoplastic organic solvent-soluble filaments. They arecomprised of a molecular structure having preferential orientation ofthe molecules along the direction of the filaments. Continuous filamentsproduced by the method described for carrying out this invention willattain a spiral or helical shaped form upon subsequent relaxation. Apreferential orientation of the molecules is accomplished by divertingthe direction of extrusion of the filament-forming material whereby avariable strain is imposed across the cross-section of the filamentswhile they are still in a semi-plastic state to rearrange the spatialstructure thereof. This irregular cross-sectional distribution of themolecules comprising the filaments is responsible for permanence of thecrimped condition possessed by filaments produced in accordance withthis invention. What is meant by permanent crimp as referred to hereinis a developed crimp which is not destroyed when subjected to asubsequent heat relaxation. Once the crimp has been developed, as forexample, during a normal annealing process, it is not destroyed ifexposed to further heating during later processing such as dyeing. Afilament which possesses crimp imposed by mechanical means elongateswhen it is heat relaxed whereby the amplitude of the cn'mps is reduceduntil the filament regains its original straightness.

The present invention may be employed in the spinning of any organicsolvent-soluble, thermoplastic, fiber-forming substance by the wetspinning process wherein the direction of the newly formed filaments isdiverted at the face of the spinneret before they becomeself-sustaining. Diversion of the semi-fluid filaments is affected bymeans of a guide bar spaced near the spinneret. The guide bar may beshifted to change the angle of the filaments with respect to thespinneret. This angle may vary from 1 to 45 depending upon the amount ofcrimp required. As the angle across the face of the spinneret decreasesthe amount of crimp or curls per inch is increased. While the filamentsmay be: drawn under tension at angles ranging from 1 to 45, thepreferred range is from 10 to 30.

The filaments of this invention may be produced on any conventionalspinning machine of the Wet spinning type by making the simple andinexpensive addition of a guide means for changing the path of thefilaments being drawn from the spinneret. A single spinneret may be usedor a number of spinnerets grouped together may be used to produce thefilaments contemplated by the invention. For the purpose of illustratingthe method employed to accomplish the expected results of this inventiona single spinneret is shown in the accompanying drawing where- FIGURE 1is a diagrammatic, elevational view of a conventional spinning apparatusmodified to illustrate the invention; and

FIGURE 2 is a cross-sectional view of the spinneret illustrating thestretch differential imposed on opposite sides of a single semi-fluidfilament.

Referring to FIGURE 1, a spinneret 10 is immersed in a coagulating bath11 contained in a tub 12. A spinning solution is pumped to the spinneretthrough a pipe 13 from a source not shown. The solution is extrudedthrough the spinneret to form filaments 14. An adjustably mounted guidebar 15 is positioned near the lower level of the bath 11 on the faceside of the spinneret. The filaments 14 are drawn from the spinneret 10at an acute angle off the face thereof by a series of take-up rolls 16.Stripper bars 17 and 18 are provided to aid in the recovery of thesolvent. As the spinning solution emerges from the spinneret in asemi-fluid state, the abrupt drawing of the newly formed filaments at aclose angle across the face of the spinneret imposes a variation instrain on the opposite sides of the filaments which remains unchangedwhen they become self-sustaining. The guide bar 15 may be raised orlowered to vary the drawing angle of the filaments. If an increase inthe number of crimps per inch is desired, the bar 15 can be lowereduntil the filaments are drawn substantially parallel with the face ofthe spinneret. Obviously, if the bar is raised the amount of crimpretentivity of the filaments is correspondingly diminished.

In FIGURE 2 a fragmentary view of a spinneret face 20, depicting asingle hole 21, is illustrated for the purpose of facilitating a betterunderstanding of the phenonomena which occurs in accordance with theprinciples of this invention. As discussed herein previously, the newlyformed filaments are in a semi-liquid state at the area 22 near the face20 of the spinneret. If is referred to as being the size of the acuteangle formed between the spinneret face 20 and filament 23, it isreadily apparent that one side of the filament is stretchedsubstantially more than the opposite side, as indicated by X when 0approaches zero. Since the stretching takes place while the filament isin a semi-fluid state the molecular structure is preferentially orientedalong the longitudinal side of the filament opposite the direction ofbend whereby a permanent crimp retentivity is imparted thereto withoutexceeding its critical yield point.

The following specific example further illustrates the invention. Partsare by by weight unless otherwise indicated.

Example A spinning solution comprised of 93% acrylonitrile and 7% vinylacetate dissolved in a suitable solvent and heated to C. was spun usingthe apparatus shown in the accompanying drawing. A single spinnerethaving 3,000 holes of 3.5 mils in diameter was used for spinning abundle of 3 denier filaments at the rate of 2.3 pounds per hour. Thefilaments were drawn across the face of the spinneret at a 10 angle andcollected in an orderly manner. These filaments were subjected to anormal annealing process wherein fine, regularly spaced crimps in theform of a helix were developed in the filaments. A microscopicobservation of the individual filaments revealed that they possessed upto 1'8 crimps per inch. Thereafter the filaments were placed in acontainer of water. The water temperature was elevated to its boilingpoint and the filaments were removed from the boiling water. Afterdrying, the filaments exhibited substantially the same amount of crimpas previously.

The present process provides an inexpensive method for imparting apermanent crimp retentivity to synthetic filaments which will reduce thesteps presently used to process such filaments for utilization insubsequent processing operations in the textile industry. For example,in the manufacture of carpets from acrylic fibers, which tend toelongate when heat relaxed, serious limitations have been imposedbecause of the fact that during the dyeing process normal crimp isdestroyed. Heretofore, the fibers have been spun from pigmented dopesolutions to overcome this problem. Acrylic fibers produced inaccordance with this invention can be dyed on skeins, or products formedtherefrom may be dyed, without removing the crimp or bulk possessed bysuch products.

Although the invention has been described primarily with reference tospinning acrylic fibers by the wet spinning process, it is alsoapplicable to such thermoplastics as nylon which is melt spun. However,an attempt to spin a thermoplastic fiber-forming material by the dryspinning process proved to be unsuccessful.

It will be apparent from the above description of the process andproducts of this invention that they are susceptible to extensivemodification without departing from the spirit of the invention.Therefore, it is to be understood that the invention is not to belimited except as set forth in the following claims.

I claim:

1. The process of producing crimped, continuous filaments whichcomprises extruding a synthetic thermoplastic filament-forming materialthrough a spinneret having a plurality of orifices to form continuousfilaments, imposing a tension on said filaments in a direction rangingfrom 10 to 30 degrees with respect to the face of said spinneret, saidchange in direction occurring at the spinneret face whereby apreferential orientation of the molecular structure of the filaments isimparted thereto, and subsequently relaxing said filaments.

2. A process for producing crimped synthetic filaments from athermoplastic composition which comprises extruding said compositionthrough a spinneret to form continuous filaments, withdrawing thefilaments from the face of the spinneret at an angle to causepreferential arrangement of the molecular structure of said filaments,and heat relaxing the withdrawn filaments to develop a crimped conditionin said filaments.

3. The process of claim 2 in which the filaments are withdrawn underuniform tension at an angle of less than 45 degrees with respect to theface of the spinneret.

4. The process of claim 3 in which the filaments are wet-spun.

5. The process of claim 4 in which the composition is comprised of atleast 80 percent acrylonitrile.

6. A process for producing continuous filaments from a thermoplasticcomposition which comprises extruding said composition through aspinneret into a liquid coagulating bath to form continuous filaments,imposing a tension on said filaments at the face of the spinneret at anangle thereto so that substantially more stretch is imparted to one sideof the filaments, said stretch being variable across the cross-sectionalarea thereof, and heat relaxing the stretched filaments to impart crimpthereto.

7. The process of claim 6 in which the composition is comprised of atleast 85 percent acrylonitrile.

8. The process of claim 7 in which the filaments are tensioned uniformlyat an acute angle with the spinneret.

9. The process of claim 8 in which the angle is less 15 than 30 degrees.

10. The process of claim 9 in which the direction of the filaments ischanged abruptly at the point of extrusion to impart preferentialorientation to the filaments.

References Cited UNITED STATES PATENTS 2,728,631 12/1955 Drisch et a1.264-168 FOREIGN PATENTS 759,928 2/1934 France. 917,040 1/1963 GreatBritain.

D. I. ARNOLD, Primary Examiner.

A. H. BRODMERKEL, Examiner.

H. H. MINTZ, Assistant Examiner.

2. A PROCESS FOR PRODUCING CRIMPED SYNTHETIC FILAMNETS FROM ATHERMOPLASTIC COMPOSTION WHICH COMPRISES EXTRUDING SAID COMPOSITIONTHROUGH A SPINNERET TO FORM CONTINUOUS FILAMENTS, WITHDRAWING THEFILAMENTS FROM THE FACE OF THE SPINNERET AT AN ANGLE TO CUASEPREFERENTIAL ARRANGEMENT OF THE MOLECULAR STRUCTURE OF SAID FILAMENTS,AND HEAT RELAXING THE WITHDRAWN FILAMENTS TO DEVELOP A CRIMPED CONDITIONIN SAID FILAMENTS.